The present invention relates to an X-ray detector array operative to convert incident penetrating radiation, such as X-rays and gamma-rays (hereinafter referred to generically as X-rays) into light, and is more particularly concerned with an improved array of line detectors of the general type shown in my aforementioned prior copending U.S. application Ser. No. 304,442, now abandoned adapted to be employed with a flying spot X-ray system, e.g. of the type disclosed in Stein et al U.S. Pat. No. 3,780,291 (issued Dec. 18, 1973, and reissued Sept. 2, 1975 as U.S. Pat. No. Re. 28,544 for "Radiant Energy Imaging With Scanning Pencil Beam"), or with other types of X-ray systems employed for medical diagnostic purposes.
The system shown in the aforementioned Stein et al patent comprises an X-ray source the output of which is collimated by a stationary slit and a cooperating rotating disc having slits therein, to produce a pencil beam of X-rays which scans in a linear direction across an object being examined. X-rays which pass through said object are detected by an elongated detector which is oriented in the scan direction and which is operative to generate output signals representative of the X-ray opacity of the object in the line of scan. Multiple such lines are generated by translating the X-ray source/detector arrangement and/or the object being examined relative to one another in a direction transverse to the scan direction thereby to produce groups of signals which can be processed and used to achieve a two-dimensional image of the X-ray opacity of the object being examined.
My prior copending application Ser. No. 304,442, the disclosure of which is incorporated herein by reference, discloses an improved line detector which can be used in such an X-ray inspection system, and which is adapted to convert a line beam, pencil beam, or scanning pencil beam of X-rays into an electronic signal with a one-hundred-percent detection of the X-rays. The detector comprises an elongated tubular member fabricated of an X-ray transparent material having an interior surface which is reflective to optical photons, and which supports an elongated thin planar scintillator the plane of which is oriented at an acute angle to the direction of the beam whereby the path of the X-rays through the scintillator is longer than the thickness of the scintillator. Optical photons which are emitted by the scintillator are reflected by the interior surface of the tubular member to a photomultiplier tube which is disposed adjacent at least one end of the detector. This detector arrangement allows the use of an X-ray scintillating material which is an efficient absorber of X-rays, has very little optical afterglow, and/or which exhibits unique absorption characteristics for a specific energy of X-rays, but which, at the same time, may be a poor transmitter of visible light either because it is not very transparent, or because the scintillator material is in the form of a powder as in a conventional X-ray intensifier screen.
The present invention relates, inter alia, to a novel array of detectors of the general type described in said prior application Ser. No. 304,442, which achieves a number of advantages. More particularly:
a. The energy collected from the X-ray source is increased by a factor equal to the number of detector pairs employed in the array, thereby producing an increase in collection efficiency which may be used to improve the spatial resolution since data are taken simultaneously in each of the detectors, so that each detector may define a smaller pixel size;
b. Alternatively, the extra energy may be used to achieve higher density resolution by increasing the exposure;
c. Alternatively, the improved efficiency of collection may be used to decrease the time of exposure to the subject, e.g. the time of exposure can be decreased by a factor equal to the number of detector pairs which are employed in the array;
d. Since each of the detectors in the array views the entire subject, the problem of matching the detectors to one another is eliminated, i.e., in contrast to other systems suggested heretofor which utilize a row of small discrete detectors, it is not necessary in the present invention to normalize (i.e. match the response) of every detector at every signal height to avoid "lines" in the final image; and
e. Since the several detectors in the array each produce an output signal representative of the entire subject, the signals from the several detectors can be combined in selected ways to provide various kinds of information regarding the X-ray opacity of the object being examined.